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<Paper uid="W96-0416">
  <Title>ruta, &amp;quot;Petri-net based Hypertext: Document Structure with Browsing Semantics&amp;quot;, A CM Transactions on Information</Title>
  <Section position="1" start_page="0" end_page="152" type="abstr">
    <SectionTitle>
Abstract
</SectionTitle>
    <Paragraph position="0"> 'Dynamic hypertext' is hypertext which is automatically generated at the point of need. A number of NLG systems have now been developed to operate within a hypertext environment; and now that these systems are becoming widely available on the World Wide Web, it is useful to take stock of how well-equipped NLG technology is to work in this new domain. A generation system in a hypertext environment faces a specific set of requirements; here, we discuss those requirements, and the resources that can be provided to help meet them. Examples are drawn from a number of systems, including our own prototype, ILEX0. We conclude by indicating that the major benefit of such systems could be in the way that they combine flexibility with the illusion of user control.</Paragraph>
    <Paragraph position="1"> Keywords: content selection, text planning, applications, hypertext</Paragraph>
    <Section position="1" start_page="0" end_page="151" type="sub_section">
      <SectionTitle>
1.1 Static vs Dynamic Hypertext
</SectionTitle>
      <Paragraph position="0"> Within the last ten years there has been a upsurge of interest in hypertext as a medium for on-line access to written documents. As a central objective of Natural Language Generation (NLG) is on-line creation of written document~, it is hardly surprising that a number of generation systems have been developed which use hypertext as their interface.</Paragraph>
      <Paragraph position="1"> Conventional hypertext is static, in the sense that--even though each reader may  sample different parts of it--once a hyper-document has been constructed by its authors, its content and form do not change. However, applying NLG to hypertext allows the possibility of dynamic hypertext, where the document is created as demanded by the user. This approach allows the hypertext pages seen by the user to be customised in relation to the browsing context.</Paragraph>
      <Paragraph position="2"> In some cases, customisation is only in relation to content--the page brings together information from various on-line sources, but presents it in a single standard way. Other systems, using more advanced NLG techniques, allow the text to be customised in terms of both content and presentation form, being sensitive to such factors as the user model (characteristics of the user), the discourse history (a record of information presented so far), and the system's goals (what the system means to achieve).</Paragraph>
      <Paragraph position="3"> Amongst the latter systems, the degree of flexibility supported by the text generation component varies considerably. In some systems (such as StrathTutor \[Kibby and Mayes 1988\]) and Trellis \[Stotts and Furuta 1989\]), the hypertext pages are hand-crafted in advance, but the way they are linked together varies from session to session depending on the interests of the user. In other systems, the hypertext pages themselves are generated at runtime, as well as the links between them. In many current systems, a mixture of these two methods is employed.</Paragraph>
      <Paragraph position="4"> Clearly, there are many different ways of introducing flexibility into a hypertext system. Our concern in this paper is to outline the most important of these, indicating which have already been explored, and which others deserve 2 A sample domain: Museum closer attention within the NLG community, guided tours</Paragraph>
    </Section>
    <Section position="2" start_page="151" end_page="152" type="sub_section">
      <SectionTitle>
1.2 Existing Dynamic Hypertext
Systems
</SectionTitle>
      <Paragraph position="0"> A number of hypertext systems incorporating NLG technology have already been developed.</Paragraph>
      <Paragraph position="1"> In this paper, we will make reference to the five systems listed below.</Paragraph>
      <Paragraph position="2"> ALFRESCO \[Carenini et al. 1993\]: provides an interface to a videodisc of Italian frescoes and monuments. It supports natural language input and output, and generated text contains hypertext links into an existing static hypertext.</Paragraph>
      <Paragraph position="3"> IDAS \[Reiter at al. 1995, Reiter et al. 1992\]: delivers simple technical documentation online via a hypertext interface.</Paragraph>
      <Paragraph position="4"> MIGRAINE \[Buchanan et al. 1995\]: generates information and reactive explanations for a patient, based on their medical record.</Paragraph>
      <Paragraph position="5"> PEBA-II \[Dale and Milosavljevic 1996, Milosavljevic et al. 1996\]: interfaces with a zoological database. Delivers either a description of a single user-selected animal, or a comparison between two user-selected animals.</Paragraph>
      <Paragraph position="6"> PIGLIT \[Binsted et al. 1995\]: allows a patient to interface to their medical records, and receive personalised explanation.</Paragraph>
      <Paragraph position="7"> In addition to these systems, we will introduce our own prototype system ILEX-0, which is being developed specifically to examine issues arising in the domain of dynamic hypertext. The system is designed to simulate the interaction of a museum tour guide and a browsing visitor; this interaction is described in more detail in Section 2. In Section 3, the browsing task provides the context for a general discussion of the factors which influence the ability of a hypertext system to function dynamically, and in the light of this discussion, some observations about existing dynamic hypertext systems. Section 4 then --traws some conclusions concerning the real potential of dynamic hypertext.</Paragraph>
      <Paragraph position="8"> A central attraction of the hypertext interface is its suitability for the task of information browsing. By following hyperlinks, the information seeker (i.e. the user) can easily navigate to new areas of interest. At the same time, for the reasons already mentioned, there are advantages in being able to provide the information requested by the user in a dynamic fashion. If we look for an analogy in the real world to the kind of interface we are aiming for, an interesting candidate is the dialogue between a museum tour guide and a browsing visitor. The ILEX (Intelligent Labelling Explorer) project has been set up to study this domain, and to reproduce some of its distinctive features in a hypertext system. To achieve this goal, our system must: Support mixed initiative dialogue There is a degree of 'dialogic' interaction between the tour-guide and the visitor.</Paragraph>
      <Paragraph position="9"> While there are quite restricted directions that the conversation can take, each party can take the initiative in pursuing a direction.</Paragraph>
      <Paragraph position="10"> Be interesting The visitor is free to ask about whichever objects take his fancy; if an object does not hold his interest, he will move on to another, or finish.</Paragraph>
      <Paragraph position="11"> Be informative The system has all the information, and has the goal of getting across some basic messages about the content of the gallery.</Paragraph>
      <Paragraph position="12"> Clearly, the system needs to alter its descriptions in the light of the objects the visitor has already heard about, and to have some idea about what the visitor might find interesting. This is an increase in functionality compared to existing static museum hypertexts, for instance as created in the UK by the Hunterian Museum and the National Gallery.</Paragraph>
      <Paragraph position="13"> Our peint of departure has been to gather transcripts of real guided tours, in collaboration with the National Museums of Scotland. We ran two 'Curator-of-Oz' interviews, where a curator of the modern jewellery gallery was  V: Can we look at Case number 7 now, object number 10, this one here... C: Yes: you've made a link with the first piece that we looked at, which is the idea of a piece of jewellery which is also a work of art and a sculpture... [describes jewellery].</Paragraph>
      <Paragraph position="14"> l/: Can you say more about that object'? C: Yea. This one was made by Roger Morris. [Describes jeweller]. V: So is there any other object which is particularly relevant to this one'? C: Yes... [points out and describes two other brooches]. It was work like this which directly inspired work like the Roger Morris brooch we looked at earlier.  KR+Canned Full+Canned Initially Yes User Initially No KR+Intermed. Full+Template Locally Yes User Yes No KR+Canned Template No Yes User Yes Yes KR+Canned Template No? Yes System No No KR Template Yes Yes Mixed Yes Yes KR+Annot Template Some Yes Mixed No Yes  guistic Sophistication (Section 3.1), Sensitivity to Discourse History (Section 3.2), User Modelling (Section 3.3), Location of Goals (Section 3.5), Many Texts and Many Options (Section  asked to talk about a series of objects in response to simple prompts from a visitor. Figure 1 shows an extract from one such interview. V is the visitor, and C is the curator. Based on the information extracted from these tours, and additional database material, a prototype system ILEX-0 generates hypertext pages; for a sample page, see Figure 2.</Paragraph>
      <Paragraph position="15"> ILEX-0 is still far from generating discourse of the sophistication shown by a real museum curator. But it should be clear that any hypertext system designed to simulate such discourse must make use of a dynamic generation component of some sort. In the following section, we consider the kinds of flexibility which this component should ideally provide.</Paragraph>
    </Section>
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